Testing length-scale considerations in mechanical characterization of WC-Co hardmetal produced via binder jetting 3D printing

The extreme versatility of additive manufacturing (AM) as processing technology results in “AMed pieces” with intrinsic characteristics linked to the shaping route followed, which are also key for defining mechanical integrity. The latter requires validation by measuring the mechanical properties, at both macroscopic (global) and microscopic (local) levels; and thus, consideration of specific testing length-scale aspects. This work aims to study the correlation between microstructure and mechanical properties for a WC-12%wt.Co hardmetal grade produced via binder jetting 3D printing (BJT) and subsequent sintering. In doing so, macro- and micro- Vickers hardness as well as scratch tests, using different loads and indenter tips, are conducted. It is found that studied samples processed by means of BJT exhibit a microstructure consisting of a relatively wide carbide size distribution, including a significant volume fraction (higher than 15%) of carbides larger than 3 µm. This is a direct consequence of the relatively high sintering temperature needed for getting full dense specimens, when manufactured following this AM route. Meanwhile, mechanical properties are found to be isotropic, with hardness and scratch resistance values falling within ranges of those expected for hardmetals with similar binder content and mean carbide grain size. Very interesting, length-scale effects on testing are observed in terms of dispersion of measured hardness value as applied load decreases. These findings, together with similar ones linked to length-scale influence on scratch response, point out that effective selection of mechanical testing parameters become critical for studying and understanding phenomena such as elastic/plastic and deformation/fracture transitions in AMed hardmetals.Peer ReviewedPostprint (published version

Influence of printing direction on the mechanical properties at different length scales for WC-Co samples consolidated by Binder Jetting 3D printing

Additive Manufacturing (AM) is rapidly growing as a revolutionary technique. It provides an interesting ability to produce complex geometries, a key feature for enhancing performance and widening application fields of hardmetal components. Within this context, all the samples produced by AM [AMed] are expected to exhibit characteristics linked to the shaping route followed, which are also vital for defining their mechanical integrity. This work aims to study the correlation of the printing direction to the final microstructure, mechanical properties and layer assemblage at different length scales for a 12%wtCo–WC grade hardmetals of medium grain size consolidated by binder jetting 3DP and subsequent SinterHIP. Vickers macro- and micro-hardness as well as scratch tests, using different loads and indenter tips, are conducted. The results are analysed and discussed in terms of printing orientation effects on microstructural variability, mechanical response determined, intrinsic physical behaviour of the material and feedstock used.Postprint (published version

Antibody Production in Murine Polymicrobial Sepsis—Kinetics and Key Players

Although antigen-specific priming of antibody responses is impaired during sepsis, there is nevertheless a strong increase in IgM and IgG serum concentrations. Using colon ascendens stent peritonitis (CASP), a mouse model of polymicrobial abdominal sepsis, we observed substantial increases in IgM as well as IgG of all subclasses, starting at day 3 and peaking 2 weeks after sepsis induction. The dominant source of antibody-secreting cells was by far the spleen, with a minor contribution of the mesenteric lymph nodes. Remarkably, sepsis induction in splenectomized mice did not change the dynamics of the serum IgM/IgG reaction, indicating that the marginal zone B cells, which almost exclusively reside in the spleen, are dispensable in such a setting. Hence, in systemic bacterial infection, the function of the spleen as dominant niche of antibody-producing cells can be compensated by extra-splenic B cell populations as well as other lymphoid organs. Depletion of CD4+ T cells did not affect the IgM response, while it impaired IgG generation of all subclasses with the exception of IgG3. Taken together, our data demonstrate that the robust class-switched antibody response in sepsis encompasses both T cell-dependent and -independent components

Oxidation-Specific Epitopes (OSEs) Dominate the B Cell Response in Murine Polymicrobial Sepsis

In murine abdominal sepsis by colon ascendens stent peritonitis (CASP), a strong increase in serum IgM and IgG antibodies was observed, which reached maximum values 14 days following sepsis induction. The specificity of this antibody response was studied in serum and at the single cell level using a broad panel of bacterial, sepsis-unrelated as well as self-antigens. Whereas an antibacterial IgM/IgG response was rarely observed, studies at the single-cell level revealed that IgM antibodies, in particular, were largely polyreactive. Interestingly, at least 16% of the IgM mAbs and 20% of the IgG mAbs derived from post-septic mice showed specificity for oxidation-specific epitopes (OSEs), which are known targets of the innate/adaptive immune response. This identifies those self-antigens as the main target of B cell responses in sepsis

Karies- und Erosionsschutz durch Thymian? In vitro und in situ Untersuchungen zur Wirksamkeit

Thyme for caries and erosion protection? In vitro and in situ investigations for efficacy testin

Reduced Numbers and Impaired Function of Regulatory T Cells in Peripheral Blood of Ischemic Stroke Patients

Background and Purpose. Regulatory T cells (Tregs) have been suggested to modulate stroke-induced immune responses. However, analyses of Tregs in patients and in experimental stroke have yielded contradictory findings. We performed the current study to assess the regulation and function of Tregs in peripheral blood of stroke patients. Age dependent expression of CD39 on Tregs was quantified in mice and men. Methods. Total FoxP3+ Tregs and CD39+FoxP3+ Tregs were quantified by flow cytometry in controls and stroke patients on admission and on days 1, 3, 5, and 7 thereafter. Treg function was assessed by quantifying the inhibition of activation-induced expression of CD69 and CD154 on T effector cells (Teffs). Results. Total Tregs accounted for 5.0% of CD4+ T cells in controls and <2.8% in stroke patients on admission. They remained below control values until day 7. CD39+ Tregs were most strongly reduced in stroke patients. On day 3 the Treg-mediated inhibition of CD154 upregulation on CD4+ Teff was impaired in stroke patients. CD39 expression on Treg increased with age in peripheral blood of mice and men. Conclusion. We demonstrate a loss of active FoxP3+CD39+ Tregs from stroke patient’s peripheral blood. The suppressive Treg function of remaining Tregs is impaired after stroke

B-Zellreaktionen und das humorale Immungedächtnis bei muriner polymikrobieller Sepsis

Trotz großer Verbesserungen bei der intensivmedizinischen Behandlung ist das Krankheitsbild Sepsis auch heute noch mit erschreckend hoher Morbidität und Letalität assoziiert. Ob B-Zellen in der Sepsis eine Rolle spielen und wie das adaptive humorale Immunsystem insgesamt durch Sepsis beeinflusst wird, wurde bisher wenig erforscht. Weil bei einer Sepsis viele Immunzellen in Apoptose gehen und die Immunantwort insgesamt supprimiert ist, wurde bisher angenommen, dass nach Sepsis auch die B-Zellantwort vermindert ist. Die Befunde dieser Arbeit zeigen, dass das adaptive Immunsystem bei polymikrobieller Sepsis entgegen den Erwartungen initial nicht supprimiert war. B-Zellen der Milz wurden sehr früh aktiviert. Es kam zur Keimzentrums- und Plasmazellbildung, infolgedessen die IgM- und IgG-Konzentrationen im Serum anstiegen. Darunter befanden sich selbstreaktive Antikörper, die allerdings keine Symptome einer Autoimmunerkrankung auslösten. Produzenten dieser Antikörper waren vermutlich B1-Zellen, die B-Zellrezeptorunabhängig, also polyklonal, aktiviert wurden. T-Zellen konnten sehr früh nach Sepsis antigenspezifisch aktiviert werden, und waren für einen Teil der B-Zellantwort nach Sepsis notwendig. Später war die antigenspezifische Primärantwort der T-Zellen eingeschränkt. Obwohl die Milz und die in der Maus dort ansässigen Marginalzonen-B-Zellen entscheidend an der Abwehr von Infektionen beteiligt sind, schienen sie für die Antikörperproduktion entbehrlich zu sein. Eine weitere wichtige Erkenntnis dieser Arbeit ist, dass Sepsis mit dem humoralen Immungedächtnis interferierte. Ob dies allerdings den Immunschutz beeinträchtigt, kann nicht abschließend geklärt werden. Klinische Studien konnten einen Einfluss einer Sepsis auf die humorale Immunität beim Menschen weder bestätigen noch ausschließen. Nach schwerer Operation allerdings schien das Immungedächtnis in Form antigenspezifischer Antikörper verstärkt.Severe sepsis is associated with high morbidity and mortality and has a poor long-term prognosis. Acute sepsis in mice is characterised by an increase in apoptotic cells and a generalised suppressed immune response. Therefore, it was unclear, whether B-cells become activated in the course of sepsis at all. This work demonstrates that the adaptive immune system was not suppressed initially. On the contrary, there was a lot of B cell activation and plasma cell differentiation, resulting in a marked increase in serum antibody concentration. Although the spleen and the resident marginal zone B cells have an important function in defence against bacteria, they seemed to be redundant for antibody production. Another important finding was that sepsis interfered with humoral memory. It remains unclear, whether this impairs the protective effect of serological memory

Manufacturing and properties of tungsten carbide-oxide composites

Conventional WC-Co hardmetals are widely used in various applications due to their excellent properties. High hardness can be achieved using compositions with little to no content of cobalt or nickel. These binder metals are hazardous to health, making a substitution not only desirable because of availability and cost reasons. A new possibility to manufacture such hard materials is the combination of tungsten carbide with oxides such as Al2O3 and ZrO2. In this way the binder metal content can be replaced. Furthermore the content of the also expensive WC can be reduced. Such metal carbide – oxide composites with oxide contents between 16 vol% and 40 vol% were manufactured. The completely dense composites feature high hardness values of 2000 HV10 to 2400 HV10 while also having an acceptable fracture toughness of up to 7 MPa⋅m1/2. The improved mechanical properties make the replacement of WC-Co hardmetals and binder free WC ceramics in special areas possible

Correlation of Different Cemented Carbide Starting Powders with the Resulting Properties of Components Manufactured via Binder Jetting

For several years, researchers have been exploring the use of the binder jetting powder-based additive manufacturing process to produce WC-Co hardmetals. Compared to other additive manufacturing processes, binder jetting has the potential for high-volume production. However, due to the powder-based approach, the resulting green bodies typically have low green density, limiting the achievable hardness and requiring higher Co content. Choosing the appropriate starting powder and post-processing can extend previous limitations and allow the selection of a suitable powder based on the application. This investigation focuses on exploring and evaluating the correlation between varying morphologies of WC-Co starting powders, their processability using the BJT method, and the resultant mechanical properties of sintered components

Properties of Additive Manufactured Hardmetal Components produced by Fused Filament Fabrication (FFF)

Additive Manufacturing (AM) is experiencing an upswing in many sectors of industry for a broad variety of materials. Processes are mainly developed for polymers and metals. For ceramics and especially hardmetals there are only a few additive processes suitable to produce dense and defect free parts. Fused Filament Fabrication (FFF) is one of the suitable processes, which can be used for the fabrication of hardmetal parts via printing of green parts and consequent sintering. Within this study FFF of different hardmetal compositions representing different Co binder contents and different WC grain sizes are investigated. Main points of this investigation are the adjustment of debindering using different thermal and non-thermal steps and the adjustment of sintering regime. It is shown that FFF is a suitable AM technique for production of hardmetal parts with different compositions and microstructures. Dense parts with magnetic and mechanical properties as conventional produced hardmetals can be achieved. It is shown that with the Fused Filament Fabrication fully dense and defect free hardmetals parts can be produced. Because of the thermoplastic processability of the filaments which can be highly filled with particles this technique is interesting for manufacturing hardmetal parts